1 The Development of a Marble Clear Gel Coat with Improved

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1 The Development of a Marble Clear Gel Coat with Improved Powered By Docstoc
					COMPOSITES & POLYCON 2007                                         drop-off in thermal cycle test results. ANSI Z124.3 re-
American Composites Manufacturers Association                     quirements for cultured marble lavatories specify that the
October 17-19, 2007                                               part shall surpass 500 cycles in thermal shock testing
Tampa, FL USA                                                     without failure. It was found that many of these initial
                                                                  marble clears could pass the requirement, but barely.
                                                                  Failures at 600-800 cycles were typical while the con-
                                                                  ventional marble clear products with higher HAP con-
    The Development of a Marble Clear Gel                         tents would typically surpass 1000 cycles in testing.
Coat with Improved Performance Properties
                                                                             With the correction of these deficiencies in
                                                        by        mind, a development project was initiated. Early on in
                                                                  the development, it was recognized that in order to elimi-
                                         Daniel A. Oakley         nate many of the shortcomings in the initial clear gel
                                                    AOC           coats, a new polymer would need to be at the forefront of
                                                                  the development. With this new technology, the formu-
                                                                  lating of a new clear gel coat could be optimized to
                                                                  achieve the necessary process and performance charac-
Abstract                                                          teristics.
         This paper describes the development and opti-
mization of a clear gel coat with improved performance
in thermal cycle testing, color, and cure characteristics.        Development Process
The entire process will be outlined beginning with the
development of a new polyester resin as the backbone of
                                                                            There were four specific goals in the develop-
the new clear and ending with an illustration of the final
                                                                  ment of the new clear gel coat technology for the cast
performance and processing characteristics of the new
                                                                  polymer industry:
                                                                       • Improve the cure of the product such that manu-
                                                                            facturing cycle times can be decreased
                                                                       • Reduce the surface tack on the back side of the
Introduction                                                                clear
                                                                       • Improve thermal cycle test results
          The clear gel coat is an essential component in
                                                                       • Improve the color and clarity of the clear
the construction of cultured marble products. It must
                                                                  These goals needed to be achieved while maintaining the
provide the needed durability for years of use by the con-
                                                                  ability to formulate products with low HAP content. The
sumer, yet it must not make a visible color contribution.
                                                                  cost structure of the new technology could not be signifi-
The lack of color contribution is important so that the
                                                                  cantly higher than what was typically available on the
beauty of the matrix substrate can remain vibrant and
colorful. For the cultured marble manufacturer, the clear
gel coat must process effectively in their facility. The
                                                                            Once these goals had been determined, a poly-
clear should give acceptable spray characteristics, sag
                                                                  mer synthesis program was undertaken where several
control, air release, and leveling. It should also provide
                                                                  potential chemistries were to be investigated. Minimum
cure characteristics that allows short manufacturing cycle
                                                                  base resin mechanical properties were specified along
times for high volume production.
                                                                  with a maximum APHA color of 40. Potential candi-
                                                                  dates were synthesized and those that successfully met
         Many of the initial clears gel coat formulated to        the physical property and color criteria were formulated
meet the Composites MACT standard were found to be                into a standard clear gel coat formulation with a nominal
deficient in several key aspects. Though they met the             HAP content of 42%. An array of tests was performed
requirement of having HAP levels under 44%, the vari-             on these formulated products including tests for cure and
ous products would tend to be difficult to process under          color which were two of the primary development goals.
normal manufacturing conditions. They would also                  Other examples of this initial testing were rheology stan-
show some inferior performance characteristics as com-            dards that indicated whether the coatings would meet
pared to conventional clear gel coats with higher HAP             general processing requirements such as acceptable spray
contents. Examples of some of the process-related defi-           characteristics, sag control and air release.
ciencies were difficulties in achieving fast cure cycles
without excessive surface tackiness and difficulties in                    For any of the base resin candidates that met the
achieving good spray characteristics. Inferior perform-           cure and color goal, the next step in the process was the
ance characteristics were typically seen with a higher de-        manufacture of a typical bathroom lavatory using a stan-
gree of color contribution, a lower degree of clarity and a       dardized construction methodology. The construction of
the lavatory would also further allow the evaluation of            based on resin weight. The parts were de-molded after
the candidates spray and cure characteristics. The                 cure and allowed to post-cure for a minimum of two
manufactured lavatory was then tested on a thermal cycle           weeks prior to thermal cycle testing.
tester in accordance with the ANSI Z124.3 test parame-
ters.                                                                         Thermal cycle testing in accordance with ANSI
                                                                   Z124.3 was performed on these lavatory test bowls using
          The entire process was optimized and repeated            the apparatus shown in Figure 5. The basic principle in
numerous times until a base resin was developed that al-           the test is cycling hot and color water over the same por-
lowed the primary goals to be met. The final step in the           tion of the bowl area. A periodic visual inspection of the
development process was the optimization of the clear              bowl is done to look for any cracking in the gel coat or
gel coat formulation itself to give the best overall process       matrix. The ANSI Z124.3 requirement stipulates that the
and performance characteristics.                                   units need to cycle 500 times without defect.

Experimental                                                       Results

          The base resin synthesis program consisted in                      The R4, R8 and R10 based clear gel coats tested
maintaining an isophthalic base to the acid side of the            on the thermal cycle tester all exhibited good results with
polymer. The variants tested were changes to the glycol            gel coat failure taking place after 1000 cycles. Based on
side of the polymer formulation where the type and                 the overall positive results of cure, color, and thermal
amount of glycol was altered. The changes were made                cycle testing, it was decided to further pursue the new
with the idea that improvements could be realized in the-          polymer technology of R4. Additional lab and produc-
rmal cycle test results by an improvement in mechanical            tion scale-up of the chemistry was undertaken with con-
properties of the resin. It was also theorized that these          tinued repetition of making lavatory tops and repeated
changes would generate a better cure with a reduction in           thermal cycle testing. Figure 6 illustrates the average
air inhibition characteristics. This would give less sur-          number of cycles to failure of the newly developed tech-
face tackiness on the back side of the gel coat film. Dif-         nology as compared to the initial generation of the low
ferent methodologies of synthesis were also investigated           HAP clear gel coats.
for their effect on polymer properties and initial color.
Once produced, the new resins were tested for mechani-                      The improvement in thermal cycle test results
cal properties and needed to meet the minimum test re-             was realized by two important factors. The first factor
sults as shown in Figure 1. Resin candidates that met the          was the change to the glycol side of the new resin tech-
minimum criteria were formulated into a clear gel coat             nology which yielded an improved toughness to the for-
using the generic formulation illustrated in Figure 2.             mulated clear. The second factor was the improvement
                                                                   in cure. The improved cure allowed an optimized pro-
           The clear gel coats were tested for wet proper-         moter system in the clear gel coat formulation. This sys-
ties including viscosity, thixotropic index, color, and            tem allowed the development of optimal mechanical
cure-related properties. Figure 3 shows the cure prop-             properties without short chaining or plasticizing the
erty comparisons of the various candidates that had met            cured polymer network.
the previous development parameters. R4, R8 and R10
were of particular interest due to their fast cure and low                    Optimization of the clear gel coat formulation
degree of surface tack. These candidates also showed               yielded a product with virtually no air inhibition that re-
acceptable rheological properties and initial color charac-        sults in surface tackiness on the back side of the coating.
teristics.                                                         This allowed a substantial reduction in cure times with
                                                                   the ability to pour matrix behind the gel coat brought
          Cultured marble lavatory tops were produced              down to 30 minutes at a 77 °F ambient temperature. The
from these candidates using airless, air-assist spray              improvement in color between the initial low HAP prod-
equipment. The tool shown in Figure 4 was used to pro-             ucts and the new technology is illustrated in Figures 7
duce the parts. During the application of the clear, the           and 8. The new technology has a lower L value which
material was evaluated for ease of spray, sag control, air         means it is lighter in appearance over the white substrate
release, defect formation, and cure. The gel coat was ap-          than the initial low HAP products. Visually this corre-
plied from 18-22 mils wet using a standard MEKP initia-            lates to a sharper image of the substrate with better clar-
tor at 1.8%. The gel coat was allowed to cure and a                ity. The new technology also has a significantly lower
standardized matrix was poured behind it. A general pu-            b* value which correlates to an appearance that is much
rpose casting resin was used at a calcium carbonate filler         less yellow. These improvements in color and clarity
loading of 75%. Titanium dioxide was used at a 1%                  were realized through the low initial color from the new
loading and the system was initiated at 1.5% MEKP
polymer along with the optimization of the formulated
clear promoter system.


          This development program has demonstrated
the technology to formulate a new generation of clear gel
coats capable of meeting the Composites MACT stan-
dard. Several improvements have been made over initial
technologies where significant gains in product durabil-
ity can be obtained via improved thermal cycle test re-
sults. Additional improvements include the color and
appearance of the clear as well as improvements in proc-
ess characteristics with the ability to shorten manufactur-
ing part cycle times via faster cure.


                                                                                Daniel A. Oakley
                                                                         Gel Coat Product Leader
                                                                    Over 22 years R&D, technical
                                                                    service and manufacturing ex-
                                                                  perience in the composites coat-
                                                                                    ings industry.

Figure 1

Minimum Cast Mechanical Proper-

       Test           Units    ASTM
 Flexural Strength     Psi     D-790       12000
 Flexural Modulus     Mpsi     D-790        300
 Tensile Strength      Psi     D-638       8000
 Tensile Modulus      Mpsi     D-638        300
    Elongation         (%)     D-638        3.5
  Heat Distortion      (oC)    D-648         70
   Izod Impact        lbs/in   D-4812        1.5
 Barcol Hardness     (934-1)   D-2583        35

Figure 2

Standard Marble Clear Formulation

              Ingredient                  %
Base Resin (70% solids)                  79.50
Air Release Additive                      0.30
Fumed Silica                              1.60
Cobalt 12%                                0.05
Secondary Promoters                       0.10
Inhibitors                                0.05
Thixotropic Synergist                     0.20
Styrene Monomer                          18.20
Total:                                  100.00

       Figure 3

Cure Data

Base   Gel Time   Peak Exo-        Gel To       Thin Film   Pour Up      Tack    General Comments
       (min)      therm (oC)       Peak (min)   Gel (min)   Time (min)   Free
R1     2.5        210.2            5.2          15          25           50      Surface tack remains
R2     2.6        210.9            5.6          20          35           60      Surface tack remains
R3     2.4        220.4            4.8          10          22           50      Surface tack remains
R4     8.0        219.0            7.3          22          35           55      Tack free
R5     18.0       204.1            9.0          24          45           70      Surface tack remains
R6     6.3        211.0            7.6          20          40           65      Surface tack remains
R7     9.9        210.4            8.0          10          25           50      Surface tack remains
R8     6.1        212.0            8.0          12          25           40      Tack free
R9     9.9        211.3            7.3          22          80           120     Tack free
R10    8.0        204.8            9.6          20          35           55      Tack free
R11    14.8       200.1            9.9          35          55           120     Tack free
R12    8.2        215.1            6.9          20          60           120     Surface tack remains
R13    10.5       210.0            8.3          25          60           180     Surface tack remains
R14    23.2       197.9            15.0         50          90           120     Surface tack remains

       Figure 4

Figure 5

Figure 6

                         Marble Clear Thermal Cycle Testing

                                                            Initial          New Technology

    0      200   400   600            800   1000     1200             1400

Figure 7

                                    Marble ClearColor Difference - Lightness/Darkness

                                                                                                               New Technology


     80.0   82.0    84.0     86.0     88.0           90.0         92.0         94.0             96.0         98.0        100.0

Figure 8
                                 Martble Clear Color Difference - Yellowness

                                                                                      New Technology


    0.0     0.2    0.4     0.6      0.8        1.0          1.2          1.4           1.6             1.8


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